having made tons of cycling clothes, and being familiar wit the italian lycra that SF sells... here's my 2¢
You have to have a wicking component ( ie polyester or supplex type nylon) in order to get wicking. Swimsuit lycra, and those italian lycras will not wick. Plus, they are really thin. I get the wicking supplex lycra from Seattle fabrics. The only time I use regular lycra, Italian or not, is for either shorts, or contrast panels. I use the supplex for the main body.
The wicking polyesters and supplex nylons I refer to are fibers that are "engineered" to move moisture away from the body at the molecular lever. Regular nylons are not.
My biggest beef with swim suit lycra,(aside from the fact that it doesn't wick) for shorts especially is that it's really stretchy and thin, therefore prone to snagging.. and for a mountain biker that just won't do. I do hve one pair of summer weight shorts that are ok.
~Irulan